package com.example.order.utils;

import org.springframework.stereotype.Component;

/**
 * @Author: songyahui
 * @Date: 2020/11/6 19:06
 * @Version 1.0
 */
@Component
public class IDWorker {
    private final static long START_STMP = 1480166465631l; //序列号占用的位数
    private final static long SEQUENCE_BIT = 12; //序列号识别占用的位数
    private final static long MACHINE_BIT = 5; //机器识别占用的位数
    private final static long DATACENter_BIt = 5; //数据中心占用的位数

    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENter_BIt);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENter_BIt;

    private long datacenterId; //数据中心
    private long machineId; //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L; //上一次时间戳

    public IDWorker(){
        this(1L,1L);
    }

    public IDWorker(long datacenterId,long machineId){
        if(datacenterId > MAX_DATACENTER_NUM || datacenterId < 0){
            throw new IllegalArgumentException("datacenterId cant't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if(machineId > MAX_MACHINE_NUM || machineId < 0){
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }
    
    public synchronized long nextId(){
        long currStmp = getNewstmp();
        if(currStmp < lastStmp){
            throw new RuntimeException("Clock moved backwards,Refusing to generate id");
        }
        if(currStmp == lastStmp){
//            相同毫秒内，序列号自增
            sequence = (sequence+1) & MAX_SEQUENCE;
//            同一毫秒的序列号已经达到最大
            if(sequence==0L){
                currStmp = getNextMill();
            }
        }else {
            sequence = 0L;
        }
        lastStmp = currStmp;
        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT //数据中心部分
                | machineId << MACHINE_LEFT //机器识别部分
                | sequence;                 //序列号部分
    }

    private long getNextMill(){
        long mill = getNewstmp();
        while (mill <= lastStmp){
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        IDWorker idWorker = new IDWorker(2,3);
        for(int i = 0;i<20;i++){
            System.out.println(idWorker.nextId());
        }
    }
}
